A standard valve cartridge has a cup-shaped housing whose end is closed by a floor plate formed with a plurality of ports, typically hot- and cold-water inlet ports and a mixed-water outlet port. Sitting atop the floor plate is a fixed valve disk having throughgoing holes matching the floor-plate ports, and sitting atop this fixed valve disk is a movable valve disk having at least one downwardly open cavity. The movable valve disk can be shifted so its cavity overlaps some or all of the holes in the fixed valve plate. A lever assembly attached to the movable valve disk and to the housing is normally displaced in one direction to vary the mix of hot and cold water fed to the outlet port and in another direction to vary the volume of flow.
As described in U.S. Pat. No. 4,921,016 of Gnauert, it is standard to fit the floor-plate ports with elastomeric seal rings. These rings are made separately and must be meticulously fitted to the ports and retained in place while the cartridge itself is installed in a valve.
In order to simplify this process, U.S. Pat. No. 4,856,556 of Mennigmann proposes a complex seal that has a pair of lips that fit against opposite faces of the floor plate and the seal is itself vulcanized to the floor plate. Thus this seal is solidly locked to the floor plate and cannot fall out during installation. Nonetheless during high-pressure use the structure loosens and frequently leaks.